Multilayer ceramic capacitor and manufacturing method of multilayer ceramic capacitor

ABSTRACT

A multilayer ceramic capacitor includes: a multilayer structure in which each of dielectric layers and each of internal electrode layers are alternately stacked, a main component of the dielectric layers being ceramic, a main component of the internal electrode layers being a metal, wherein: an existence rate of crystal grains satisfying b/a&lt;1 of crystal grains included in the internal electrode layer is 70% or more, when a thickness of the internal electrode layer is “a” and a length of crystal grains of a main component metal of the internal electrode layer in an extension direction of the internal electrode layer is “b”; and the internal electrode layer includes a grain of which a main component is ceramic.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority of the prior Japanese Patent Application No. 2017-075461, filed on Apr. 5, 2017, the entire contents of which are incorporated herein by reference.

FIELD

A certain aspect of the present invention relates to a multilayer ceramic capacitor and a manufacturing method of a multilayer ceramic capacitor.

BACKGROUND

Recently, electronic devices such as smart phones or mobile phones are being downsized. Thereby, electronic components mounted on the electronic devices are rapidly being downsized. For example, in a field of multilayer ceramic capacitors, although property is secured, thicknesses of dielectric layers and internal electrodes are reduced in order to reduce a chip size (for example, see Japanese Patent Application Publication No. 2002-343669 and Japanese Patent Application Publication No. 2013-232627).

SUMMARY OF THE INVENTION

However, as disclosed in Japanese Patent Application Publication No. 2002-343669, the internal electrode gets thicker and the internal electrode tends to be broken, as sintering of a dielectric material progresses. In this case, desirable strength of the internal electrode is not achieved. For example, a crack may occur in the multilayer ceramic capacitor because of impact during mounting.

The present invention has a purpose of providing a multilayer ceramic capacitor and a manufacturing method of a multilayer ceramic capacitor that are capable of suppressing a crack.

According to an aspect of the present invention, there is provided a multilayer ceramic capacitor including: a multilayer structure in which each of dielectric layers and each of internal electrode layers are alternately stacked, a main component of the dielectric layers being ceramic, a main component of the internal electrode layers being a metal, wherein: an existence rate of crystal grains satisfying b/a<1 of crystal grains included in the internal electrode layer is 70% or more, when a thickness of the internal electrode layer is “a” and a length of crystal grains of a main component metal of the internal electrode layer in an extension direction of the internal electrode layer is “b”; and the internal electrode layer includes a grain of which a main component is ceramic.

According to an aspect of the present invention, there is provided a manufacturing method of a multilayer ceramic capacitor comprising: a first step of forming a pattern of a metal conductive paste on a green sheet including ceramic powders, a main component of the metal conductive paste being metal powders of which an average grain diameter is 100 nm or less and of which a standard deviation of grain size distribution is 1.5 or less, the metal conductive paste including ceramic powders as a co-material, an average grain diameter of the co-material being 10 nm or less, a standard deviation of grain size distribution of the co-material being 5 or less; and a second step of baking a ceramic multilayer structure obtained by stacking a plurality of layer units obtained by the first step, wherein an existence rate of crystal grains satisfying b/a<1 of crystal grains included in an internal electrode layer obtained by sintering of the metal powders in the second step is 70% or more, when a thickness of the internal electrode layer is “a” and a length of crystal grains of a main component metal of the internal electrode layer in an extension direction of the internal electrode layer is “b”.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a partial perspective view of a multilayer ceramic capacitor;

FIG. 2 illustrates a continuity modulus;

FIG. 3A illustrates an internal electrode layer in a case where a crystal grain diameter is large;

FIG. 3B illustrates an internal electrode layer in a case where a crystal grain diameter is small;

FIG. 4A illustrates a thickness “a” of an internal electrode layer;

FIG. 4B illustrates a length “b” of a crystal grain;

FIG. 5 illustrates a manufacturing method of a multilayer ceramic capacitor;

FIG. 6A illustrates grain size distribution of a main component metal of a conductive paste for forming an internal electrode layer of examples and comparative examples;

FIG. 6B illustrates grain size distribution of a co-material of a conductive paste for forming an internal electrode layer of examples and comparative examples;

FIG. 7A and FIG. 7B illustrate SEM images of cross sections of a dielectric layer and an internal electrode layer in a stacking direction;

FIG. 7C illustrates a frequency of crystal grain 14 satisfying b/a<1;

FIG. 8 illustrates results of examples and comparative examples;

FIG. 9 illustrates results of examples and comparative examples;

FIG. 10A illustrates evaluation of transverse intensity; and

FIG. 10B illustrates evaluation results of transverse intensity.

DETAILED DESCRIPTION

A description will be given of an embodiment with reference to the accompanying drawings.

Embodiment

FIG. 1 illustrates a partial perspective view of a multilayer ceramic capacitor 100 in accordance with an embodiment. As illustrated in FIG. 1, the multilayer ceramic capacitor 100 includes a multilayer chip 10 having a rectangular parallelepiped shape, and a pair of external electrodes 20 a and 20 b that are respectively provided at two edge faces of the multilayer chip 10 facing each other. In four faces other than the two edge faces of the multilayer chip 10, two faces other than an upper face and a lower face of the multilayer chip 10 in a stacking direction are referred to as side faces. The external electrodes 20 a and 20 b extend to the upper face, the lower face and the two side faces. However, the external electrodes 20 a and 20 b are spaced from each other.

The multilayer chip 10 has a structure designed to have dielectric layers 11 and internal electrode layers 12 alternately stacked. A main component of the dielectric layer 11 is a ceramic material acting as a dielectric material. A main component of the internal electrode layers 12 is a metal material such as a base metal material. End edges of the internal electrode layers 12 are alternately exposed to a first edge face of the multilayer chip 10 and a second edge face of the multilayer chip 10 that is different from the first edge face. In the embodiment, the first face faces with the second face. The external electrode 20 a is provided on the first edge face. The external electrode 20 b is provided on the second edge face. Thus, the internal electrode layers 12 are alternately conducted to the external electrode 20 a and the external electrode 20 b. Thus, the multilayer ceramic capacitor 100 has a structure in which a plurality of dielectric layers 11 are stacked and each two of the dielectric layers 11 sandwich the internal electrode layer 12. In a multilayer structure of the dielectric layers 11 and the internal electrode layers 12, the internal electrode layer 12 is positioned at an outermost layer in the stacking direction. The upper face and the lower face of the multilayer structure that are the internal electrode layers 12 are covered by cover layers 13. A main component of the cover layer 13 is a ceramic material. For example, a main component of the cover layer 13 is the same as that of the dielectric layer 11.

For example, the multilayer ceramic capacitor 100 may have a length of 0.2 mm, a width of 0.125 mm and a height of 0.125 mm. The multilayer ceramic capacitor 100 may have a length of 0.4 mm, a width of 0.2 mm and a height of 0.2 mm. The multilayer ceramic capacitor 100 may have a length of 0.6 mm, a width of 0.3 mm and a height of 0.3 mm. The multilayer ceramic capacitor 100 may have a length of 1.0 mm, a width of 0.5 mm and a height of 0.5 mm. The multilayer ceramic capacitor 100 may have a length of 3.2 mm, a width of 1.6 mm and a height of 1.6 mm. The multilayer ceramic capacitor 100 may have a length of 4.5 mm, a width of 3.2 mm and a height of 2.5 mm. However, the size of the multilayer ceramic capacitor 100 is not limited.

A main component of the internal electrode layers 12 is a base metal such as nickel (Ni), copper (Cu), tin (Sn) or the like. The internal electrode layers 12 may be made of a noble metal such as platinum (Pt), palladium (Pd), silver (Ag), gold (Au) or alloy thereof. A thickness of the internal electrode layer 12 is, for example, 0.5 μm or less. It is preferable that the thickness of the internal electrode layer 12 is 0.3 μm or less. The dielectric layers 11 are mainly composed of a ceramic material that is expressed by a general formula ABO₃ and has a perovskite structure. The perovskite structure includes ABO_(3-α) having an off-stoichiometric composition. For example, the ceramic material is such as BaTiO₃ (barium titanate), CaZrO₃ (calcium zirconate), CaTiO₃ (calcium titanate), SrTiO₃ (strontium titanate), Ba_(1-x-y)Ca_(x)Sr_(y)Ti_(1-z)Zr_(z)O₃ (0≤x≤1, 0≤y≤1, 0≤z≤1) having a perovskite structure.

For the purpose of downsizing the multilayer ceramic capacitor 100 and enlarging the capacity of the multilayer ceramic capacitor 100, reduction of thicknesses of the dielectric layer 11 and the internal electrode layer 12 is demanded. However, when the thickness of the internal electrode layer 12 is reduced, it is difficult to maintain a high continuity modulus. The reasons are as follows. In a case where the internal electrode layer 12 is formed by sintering a metal powder, when the sintering progresses, the metal powder tends to be spheroidized in order to minimize surface energy. The metal component of the internal electrode layer 12 is sintered earlier than the main component ceramic of the dielectric layer 11. Therefore, when the temperature is increased to a value at which the main component ceramic of the dielectric layer 11 is sintered, the metal component of the internal electrode layer 12 is excessively sintered and tends to be spheroidized. In this case, when there is a reason (defect) of break, the internal electrode layer 12 is broken from the defect and the continuity modulus decreases. When the continuity modulus of the internal electrode layer 12 decreases, strength of the internal electrode layer 12 may be reduced. Even if a high continuity modulus is kept, desirable strength of the internal electrode layer 12 may not be necessarily obtained when the thickness of the internal electrode layer 12 is reduced. When the desirable strength of the internal electrode layer 12 is not achieved, a crack may occur in the multilayer ceramic capacitor 100 because of mechanical shock during a mounting.

FIG. 2 illustrates the continuity modulus. As illustrated in FIG. 2, in an observation area having a length L0 in the internal electrode layer 12, lengths L1, L2 to Ln of metal portions are measured and summed. A ratio of the metal portions Σ Ln/Lo can be defined as the continuity modulus.

And so, in the embodiment, a crystal grain diameter of the internal electrode layer 12 is small. FIG. 3A illustrates the internal electrode layer 12 in a case where the crystal grain diameter is large. FIG. 3B illustrates the internal electrode layer 12 in a case where the crystal grain diameter is small. As illustrated in FIG. 3A and FIG. 3B, when a crystal grain 14 is small, the number of crystal grain boundaries 16 is large. Thus, strength of the internal electrode layer 12 is large. In concrete, as illustrated in FIG. 4A and FIG. 4B, a thickness of the internal electrode layer 12 is expressed by a thickness “a”. A length of the crystal grain 14 in an extension direction of the internal electrode layer 12 is expressed by a length “b”. In this case, an existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 is 70% or more. For example, the extension direction of the internal electrode layer 12 is a direction from the external electrode 20 a to the external electrode 20 b. In a region where the extension direction of the internal electrode layer 12 is inclined with respect to the direction from the external electrode 20 a to the external electrode 20 b, the extension direction of the internal electrode layer 12 is a direction of the inclination. With the structure, the number of the crystal grain boundaries is sufficiently large. A grain (co-material) 15 of which a main component is ceramic is left in the internal electrode layer 12. In this case, excessive sintering of a metal component of the internal electrode layer 12 during sintering is suppressed. And a breaking of the internal electrode layer 12 is suppressed. Therefore, a continuity modulus of the internal electrode layer 12 becomes larger. When the continuity modulus of the internal electrode layer 12 becomes larger, the strength of the internal electrode layer 12 becomes larger. Accordingly, the strength of the multilayer ceramic capacitor 100 becomes larger, and a crack is suppressed.

The thickness “a” may be an average value of measured results of the thicknesses of a plurality of points in the internal electrode layer 12. For example, as illustrated in FIG. 4A, the thickness “a” is an average value of thicknesses of a plurality of points of the internal electrode layer 12 at even intervals in the extension direction of the internal electrode layer 12. The thicknesses of a specific internal electrode layer 12 may be measured. The thicknesses of each of a plurality of internal electrode layers 12 may be measured, and an average of the measured thicknesses may be used as the thickness “a”. For example, as illustrated in FIG. 4A, thicknesses of at the same points at even intervals in the extension direction of each of a plurality of internal electrode layers 12 may be measured, and an average of the measured thicknesses may be used as the thickness “a”. The length “b” may be a maximum length of each crystal grain 14 in the extension direction of the internal electrode layer 12, as illustrated in FIG. 4B.

It is preferable that the existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 is 80% or more. It is more preferable that the existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 is 90% or more.

Next, a description will be given of a manufacturing method of the multilayer ceramic capacitor 100. FIG. 5 illustrates a manufacturing method of the multilayer ceramic capacitor 100.

(Making process of a raw material powder) As illustrated in FIG. 5, a dielectric material for forming the dielectric layer 11 is prepared. An A site element and a B site element of the dielectric layer 11 are generally included in the dielectric layer 11 in a shape of sintered structure of grains of ABO₃. For example, BaTiO₃ is tetragonal compound having a perovskite structure and has a high dielectric constant. BaTiO₃ can be obtained by reacting a titanium material such as titanium dioxide with a barium material such as barium carbonate and synthesizing barium titanate. Various methods are known as a synthesizing ceramic of the dielectric layer 11. For example, a solid-phase method, a sol-gel method, a hydrothermal method and so on are known. In the embodiment, any one of them can be adopted.

Next, additive compound may be added to a ceramic powder material, in accordance with purposes. The additive compound may be an oxide of Mn (manganese), V (vanadium), Cr (chromium) or a rare earth element (Y (yttrium), Dy (dysprosium), Tm (thulium), Ho (holmium), Tb (terbium), Yb (ytterbium), Sm (samarium), Eu (europium), Gd (gadolinium) and Er (erbium)), or an oxide of Co (cobalt), Ni (nickel), Li (lithium), B (boron), Na (sodium), K (potassium) and Si (silicon), or glass.

In the embodiment, it is preferable that compound including additive compound is mixed with the ceramic grains structuring the dielectric layer 11. The resulting ceramic grains with the additive compound are calcined within a temperature range of 820 degrees C. to 1150 degrees C. Then, the ceramic grains are wet-blended with the additive compound. After that, the ceramic grains with the additive compound are dried and crushed. And, desirable ceramic powder is prepared. For example, it is preferable that an average grain diameter of the ceramic powder is 50 nm to 300 nm from a viewpoint of reducing the thickness of the dielectric layer 11. For example, the grain diameter of the resulting ceramic may be adjusted by crushing the resulting ceramic powder. Alternatively, the grain diameter may be adjusted by performing the crushing and a classifying process.

(Stacking Process) Next, a binder such as polyvinyl butyral (PVB) resin, an organic solvent such as ethanol or toluene, and a plasticizer such as dioctyl phthalate (DOP) are added to the resulting dielectric material and wet-blended. With use of the resulting slurry, a strip-shaped dielectric green sheet with a thickness of 0.8 μm or less is coated on a base material by, for example, a die coater method or a doctor blade method, and then dried.

Then, a pattern of the internal electrode layer 12 is provided on the surface of the dielectric green sheet by printing a conductive paste for forming an internal electrode layer with use of screen printing or gravure printing. The conductive paste includes an organic binder. Thus, internal electrode layer patterns that are alternately extracted to the pair of external electrodes are provided. A metal material of the metal conductive paste has an average grain diameter of 100 nm or less. A standard deviation of the grain diameter is 15 or less. In this case, sharp grain size distribution is obtained. It is preferable that the average grain diameter is 100 nm or less. It is more preferable that the average grain diameter is 70 nm or less. It is preferable that the standard deviation of the grain diameter is 15 or less. It is more preferable that the standard deviation of the grain diameter is 12 or less. An inclination of accumulated grain size distribution is 8 or more. The inclination of the accumulated grain size distribution can be defined as an inclination (=1/(log D80−log D20)) between D20 and D80 in a case where the accumulated grain size distribution is plotted in a logarithmic manner.

As a co-material, ceramic grains are added to the metal conductive paste. A main component ceramic of the ceramic grains is not limited. However, it is preferable that a main component ceramic of the co-material is the same as that of the dielectric layer 11. For example, barium titanate may be evenly dispersed. For example, ceramic grains of which an average grain diameter is 10 nm or less are used as the co-material. The standard deviation of the grain diameter is 5 or less. Thus, sharp grain size distribution is achieved. It is preferable that the average grain diameter is 15 nm or less. It is more preferable that the average grain diameter is 10 nm or less. It is preferable that the standard deviation of the grain diameter is 5 or less. It is more preferable that the standard deviation of the grain diameter is 3 or less. It is preferable that the inclination of the accumulated grain size distribution is 7 or more. The inclination of the accumulated grain size distribution can be defined as an inclination (=1/(log D80−log D20)) between D20 and D80 in a case where the accumulated grain size distribution is plotted in a logarithmic manner.

Then, the dielectric green sheet on which the internal electrode layer pattern is printed is stamped into a predetermined size, and a predetermined number (for example, 100 to 500) of stamped dielectric green sheets are stacked while the base material is peeled so that the internal electrode layers 12 and the dielectric layers 11 are alternated with each other and the end edges of the internal electrode layers 12 are alternately exposed to both edge faces in the length direction of the dielectric layer so as to be alternately led out to a pair of external electrodes of different polarizations. Cover sheets, which are to be the cover layers 13, are compressed on the stacked dielectric green sheets and under the stacked dielectric green sheets. The resulting multilayer structure is cut into a predetermined size (for example, 1.0 mm×0.5 mm). After that, a metal conductive paste, which is to be the ground layer of the external electrodes 20 a and 20 b is coated on the both edge faces of the resulting multilayer structure and is dried. Thus, a compact of the multilayer ceramic capacitor 100 is obtained.

(Baking process) Next, after removing the binder in N₂ atmosphere at 250 degrees C. to 500 degrees C., the resulting compact is baked for ten minutes to 2 hours in a reductive atmosphere, of which an oxygen partial pressure is 10⁻⁵ to 10⁻⁸ atm, in a temperature range of 1100 degrees C. to 1300 degrees C. Thus, each compound structuring the dielectric green sheet is sintered. In this manner, the multilayer ceramic capacitor 100 is obtained. When the baking condition is adjusted, the existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 can be 70% or more. In concrete, when a speed of temperature increasing in the baking process is enlarged, the main component metal is sintered before the co-material is extruded from the metal conductive paste. Therefore, the co-material tends to exist in the internal electrode layer 12. The co-material existing in the internal electrode layer 12 reduces the crystal grain diameter of the internal electrode layer 12. For example, it is preferable that the average speed of the temperature increasing from a room temperature to a maximum temperature in the baking process is 30 degrees C./minute or more in order that the existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 is 70% or more. It is more preferable that the average speed of the temperature increasing is 45 degrees C./minute or more. When the average speed of the temperature increasing is excessive large, an organic component existing in the compact (which is left after the process for removing the binder) is not sufficiently removed. And a defect such as crack in the baking process may occur. And so, it is preferable that the average speed of the temperature increasing is 80 degrees C./minute or less. It is more preferable that the average speed of the temperature increasing is 65 degrees C./minute or less. It is preferable that the existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 is 80% or more. It is more preferable that the existence ratio of the crystal grains 14 satisfying b/a<1 with respect to the crystal grains 14 included in the internal electrode layer 12 is 90% or more.

(Re-oxidizing process) After that, a re-oxidizing process may be performed at 600 degrees C. to 1000 degrees C. in N₂ gas atmosphere. (Plating process) After that, metal layers such as Cu, Ni or Su are coated on the ground layers of the external electrodes 20 a and 20 b by a plating process.

With the manufacturing method of the multilayer ceramic capacitor in accordance with the embodiment, a small diameter material of which grain size distribution is sharp is used as the main component metal of the internal electrode layer 12 and the co-material. Therefore, highly distributed metal conductive paste is obtained. And, a partial mixing of a large diameter material is suppressed. When the highly distributed metal conductive paste is used, diffusion of the co-material into the dielectric layer 11 in the baking process is suppressed. And the co-material exists in the internal electrode layer 12.

When the co-material exists in the internal electrode layer 12, excessive sintering of the metal component of the internal electrode layer 12 during sintering is suppressed. And a breaking of the internal electrode layer 12 is suppressed. Therefore, a continuity modulus of the internal electrode layer 12 becomes larger. When the continuity modulus of the internal electrode layer 12 becomes larger, the strength of the internal electrode layer 12 as a metal becomes larger. Accordingly, the strength of the multilayer ceramic capacitor 100 becomes larger, and a crack is suppressed. And, when the co-material exists in the internal electrode layer 12, the crystal grain boundaries of the main component metal of the internal electrode layer 12 becomes smaller and the number of the grain boundaries becomes larger. When the number of the crystal grain boundaries of the main component metal of the internal electrode layer 12 is large, the diameter of the crystal grains becomes smaller. Therefore, the strength of the internal electrode layer 12 as a metal becomes larger. Accordingly, the strength of the multilayer ceramic capacitor 100 becomes larger. And the crack can be suppressed.

EXAMPLES

The multilayer ceramic capacitors in accordance with the embodiment were made and the property was measured.

Examples 1 to 5

A necessary additive compound was added to a barium titanate powder of which an average grain diameter is 100 nm (a specific surface area of 10 m²/g). The resulting barium titanate powder was sufficiently wet-blended and crushed with a ball mil. Thus, the dielectric material was obtained. An organic binder and a solvent were added to the dielectric material. And dielectric green sheets were made by a doctor blade method. A thickness of the dielectric green sheet was 0.8 μm. The organic binder was polyvinyl butyral (PVB) resin or the like. The solvent was ethanol, toluene or the like. And a plasticizer and so on were added.

Next, the conductive paste for forming the internal electrode layer was formed by a planetary boll mill. The conductive paste included a main component metal (Ni) powder of the internal electrode layer 12 (50 wt % of Ni solid content), 10 weight part of a co-material (barium titanate), 5 weight part of binder (ethyl cellulose), a solvent and an auxiliary as needed. As shown in Table 1, the average grain diameter of the main component metal powder was 70 nm (a specific surface area was 10 m²/g). The standard deviation of the grain diameter of the main component metal powder was 12. The inclination of the accumulated grain size distribution was 8. The average grain diameter of the co-material was 8.6 nm (a specific surface area was 110 m²/g). The standard deviation of the grain diameter of the co-material was 2.7. The inclination of the accumulated grain size distribution of the co-material was 7.

TABLE 1 INCLINATION OF ACCUMULATED AVERAGE GRAIN GRAIN STANDARD SIZE DIAMETER DEVIATION DISTRIBUTION EXAM- MAIN   70 nm 12 8 PLES COMPONENT 1 TO 5 METAL CO-  8.6 nm 2.7 7 MATERIAL COM- MAIN  120 nm 33 6 PAR- COMPONENT ATIVE METAL EXAM CO-   29 nm 8.7 5 PLES MATERIAL 1 TO 3

The conductive paste for forming the internal electrode layer was screen-printed on the dielectric green sheet. 250 of the dielectric green sheets on which the conductive paste for forming the internal electrode layer was printed were stacked, and cover sheets were stacked on the stacked dielectric green sheets and under the stacked dielectric green sheets. After that, a ceramic multilayer structure was obtained by a thermal compressing. And the ceramic multilayer structure was cut into a predetermined size.

The binder was removed from the ceramic multilayer structure in N₂ atmosphere. After that, the metal paste including the metal filler of which a main component was Ni, the co-material, the binder and the solvent was coated from the both edge faces to the side faces of the ceramic multilayer structure and was dried. After that, the resulting multilayer structure was baked together with the metal paste for 10 minutes to 2 hours in a reductive atmosphere in a temperature range of 1100 degrees C. to 1300 degrees C. And, a sintered structure was formed. The average speed of temperature increasing from a room temperature to a maximum temperature was 30 degrees C./minute in the example 1, 45 degrees C./minute in the example 2, 55 degrees C./minute in the example 3, 65 degrees C./minute in the example 4 and 80 degrees C./minute in the example 5.

The resulting sintered structure had a length of 0.6 mm, a width of 0.3 mm and a height of 0.3 mm. The sintered structure was subjected to a re-oxidation process at 800 degrees C. in N₂ atmosphere. After that, by a plating process, a Cu-plated layer, a Ni-plated layer and a Sn-plated layer were formed on a surface of a ground layer. And, the multilayer ceramic capacitor 100 was obtained.

Comparative Examples 1 to 3

In comparative examples 1 to 3, as shown in Table 1, an average grain diameter of a main component metal powder (Ni) of the conductive paste for forming the internal electrode layer was 120 nm. A standard deviation of the grain diameters of the powder was 33. An inclination of accumulated grain size distribution of the powder was 6. An average grain diameter of a co-material was 29 nm. A standard deviation of the grain diameters of the co-material was 8.7. An inclination of accumulated grain size distribution of the co-material was 5. An average speed of temperature increasing from a room temperature to a maximum temperature was 45 degrees C./minute in the comparative example 1, 55 degrees C./minute in the comparative example 2 and 65 degrees C./minute in the comparative example 3. Other conditions were the same as those of the examples 1 to 5.

FIG. 6A illustrates grain size distribution of the main component metal of the conductive paste for forming the internal electrode layer of the examples 1 to 5 and grain size distribution of the main component metal of the conductive paste for forming the internal electrode layer of the comparative examples 1 to 3. As illustrated in FIG. 6A, in the examples 1 to 5, a metal powder of which the average grain diameter was small and of which grain size distribution was sharp was used. In the comparative examples 1 to 3, a metal powder of which the average grain diameter was large and of which the grain size distribution was broad was used. FIG. 6B illustrates the grain size distribution of the co-material of the conductive paste for forming the internal electrode layer of the examples 1 to 5 and the co-material of the conductive paste for forming internal electrode layer of the comparative examples 1 to 3. As illustrated in FIG. 6B, in the examples 1 to 5, the average grain diameter of the co-material was small, and the grain size distribution of the co-material was sharp. In the comparative examples 1 to 3, the average grain diameter of the co-material was large, and the grain size distribution of the co-material was broad.

(Analysis) FIG. 7A and FIG. 7B illustrate SEM (Scanning Electron Microscope) images of a cross section of the dielectric layer 11 and the internal electrode layer 12 in the stacking direction. FIG. 7A illustrates a SEM image of the example 4. FIG. 7B illustrates a SEM image of the comparative example 2. From the results of FIG. 7A and FIG. 7B, the thicknesses “a” of the internal electrode layers 12 and the lengths “b” of the crystal grains 14 were measured. A field of view of the SEM images was 12.6 μm×8.35 μm. For example, as illustrated in FIG. 4A, five points were determined at even intervals of 2 μm from the external electrode 20 a to the external electrode 20 b in the extension direction of the internal electrode layer 12. Thicknesses of at the same points at the even intervals in the extension direction of seven internal electrode layers 12 were measured, and an average of the measured thicknesses was used as the thickness “a”. The length “b” was a maximum length of each crystal grain 14 in the extension direction of the internal electrode layer 12 from the external electrode 20 a to the external electrode 20 b, as illustrated in FIG. 4B.

FIG. 7C illustrates a frequency of the crystal grain 14 satisfying b/a<1 in the SEM images of FIG. 7A and FIG. 7B. As illustrated in FIG. 7C, in the comparative example 2, the frequency of the crystal grain 14 satisfying b/a<1 was 0.6 (60%). On the other hand, in the example 4, the frequency of the crystal grain 14 satisfying b/a<1 was 0.9 (90%). FIG. 8 illustrates the measured frequency of the crystal grain 14 satisfying b/a<1, in the examples 1 to 5 and the comparative examples 1 to 3. FIG. 9 illustrates a table including the measured results. As illustrated in FIG. 8 and FIG. 9, in any of the examples, it was confirmed that the frequency of the crystal grain 14 satisfying b/a<1 was 70% or more. In any of the comparative examples, it was confirmed that the frequency of the crystal grain 14 satisfying b/a<1 was less than 70%.

With use of the SEM images, the continuity modulus described with use of FIG. 2 were measured. The continuity moduluses of the examples 1 to 5 were 100%. The continuity moduluses of the comparative examples 1 to 3 were 94% to 96%. The continuity moduluses were calculated by measuring the continuity moduluses of all of the internal electrode layers included in a few of SEM images and calculating an average of the measured continuity moduluses.

Next, a transverse intensity of the multilayer ceramic capacitors 100 of the examples and the comparative examples was evaluated. With respect to each 10 samples of the examples 1 to 5 and the comparative examples 1 to 3, as illustrated in FIG. 10A, the external electrode 20 a and the external electrode 20 b were supported, a load was applied to a center portion between the external electrodes 20 a and 20 b in the stacking direction of the dielectric layer 11 and the internal electrode layer 12. For example, when lower faces of the external electrodes 20 a and 20 b were supported, the load was applied from an upper side to a lower side. The load was gradually increased, and a sample in which crack occurred was determined as breakdown. An average of the load causing the breakdown of the samples of the examples 1 to 5 and the comparative examples 1 to 3 was evaluated as the transverse intensity.

FIG. 10B illustrates a graph of the evaluation results of the transverse intensity. A vertical axis of FIG. 10B indicates a load with which breakdown of the samples occurs. In FIG. 10B, averages of the load of the samples of the examples 1 to 5 and the comparative examples 1 to 3 are plotted. And, variability of the load of the samples of the examples 1 to 5 and the comparative examples 1 to 3 is indicated with an error bar. In FIG. 10B, a normalized load is illustrated on a presumption that the average of the load of the samples of the comparative examples 1 to 3 is 100%.

From the results of FIG. 10B, the variability of the transverse intensity of the samples is within ±10%. The transverse intensity of the examples 1 to 5 is increased by 10% on average with respect to that of the comparative examples 1 to 3. This is because the small diameter material of which grain size distribution was sharp was used as the metal material of the metal conductive paste for forming the internal electrode layer, the co-material existed in the internal electrode layer 12 during the sintering, the excessive sintering of the metal component of the internal electrode layer 12 during the sintering was suppressed, the break of the internal electrode layer 12 was suppressed, the strength of the internal electrode layer 12 as a metal was improved, the crystal grains were downsized, and the strength of the internal electrode layer 12 as a metal increased.

Although the embodiments of the present invention have been described in detail, it is to be understood that the various change, substitutions, and alterations could be made hereto without departing from the spirit and scope of the invention. 

What is claimed is:
 1. A multilayer ceramic capacitor comprising: a multilayer structure in which each of dielectric layers and each of internal electrode layers are alternately stacked, a main component of the dielectric layers being ceramic, a main component of the internal electrode layers being a metal, wherein: at least one of the internal electrode layers includes crystal grains whose main component is the metal, said crystal grains contacting two of the dielectric layers sandwiching the at least one of the internal electrode layers, where the at least one of the internal electrode layers further includes a grain whose main component is ceramic, said grain being enclosed in at least one of the crystal grains as viewed in a cross section in a stacking direction of the dielectric layers; the at least one of the internal electrode layers further includes a crystal boundary extending between the two of the dielectric layers, and another grain whose main component is ceramic, said another grain existing on the crystal boundary and being enclosed in the at least one of the internal electrode layers; an existence rate of crystal grains satisfying b/a<1 relative to all crystal grains included in the at least one of the internal electrode layers is 70% or more, when a thickness of the at least one of the internal electrode layers is “a” and a length of crystal grains whose main component is the metal of the at least one of the internal electrode layers in an extension direction of the at least one of the internal electrode layers is “b”.
 2. The multilayer ceramic capacitor as claimed in claim 1, wherein the main component of the at least one of the internal electrode layers is nickel.
 3. The multilayer ceramic capacitor as claimed in claim 1, wherein the main component of the grain is barium titanate.
 4. The multilayer ceramic capacitor as claimed in claim 1, wherein the main component of the dielectric layers is barium titanate.
 5. The multilayer ceramic capacitor as claimed in claim 1, wherein a thickness of the at least one of the internal electrode layers is 0.3 μm or less.
 6. A manufacturing method of a multilayer ceramic capacitor comprising: a first step of forming a pattern of a metal conductive paste on a green sheet including ceramic powders, a main component of the metal conductive paste being metal powders of which an average grain diameter is 100 nm or less and of which a standard deviation of grain size distribution is 15 or less, the metal conductive paste including ceramic powders as a co-material, an average grain diameter of the co-material being 10 nm or less, a standard deviation of grain size distribution of the co-material being 5 or less; and a second step of baking a ceramic multilayer structure obtained by stacking a plurality of layer units obtained by the first step, wherein an internal electrode layer obtained by sintering of the metal powders in the second step includes crystal grains whose main component is a metal of the internal electrode layer, said crystal grains contacting two of dielectric layers sandwiching the internal electrode layer obtained by sintering of the green sheets in the second step, at least one of the co-materials being enclosed in at least one of the crystal grains as viewed in a cross section in a stacking direction of the dielectric layers; wherein the internal electrode layer further includes a crystal boundary extending between the two of the dielectric layers, and another co-material existing on the crystal boundary and being enclosed in the internal electrode layer; wherein an existence rate of crystal grains satisfying b/a<1 relative to all crystal grains included in the internal electrode layer is 70% or more, when a thickness of the internal electrode layer is “a” and a length of crystal grains whose main component is the metal of the internal electrode layer in an extension direction of the internal electrode layer is “b”.
 7. The method as claimed in claim 6, wherein an average speed of temperature increasing from a room temperature to a maximum temperature is 30 degrees C./minute to 80 degrees C./minute in the second step.
 8. The method as claimed in claim 6, wherein a main component of the metal powder is nickel.
 9. The method as claimed in claim 6, wherein a main component of the co-material is barium titanate.
 10. The method as claimed in claim 6, wherein a main component of the ceramic powders of the green sheet is barium titanate.
 11. The method as claimed in claim 6, wherein: in the grain size distribution of the metal powders, an inclination of accumulated grain size distribution “1/(log D80−log D20)” is 8 or more; and in the grain size distribution of the co-material, an inclination of accumulated grain size distribution “1/(log D80−log D20)” is 7 or more. 